Some say the Ju of Judo is pretty Aiki-ish. Certainly Kito-ryu (one of the root arts of Judo) used the term.

Aiki was originally a kenjutus term.

Yes and no. Morihei Ueshiba stated repeatedly that his "aiki" was different from "aiki" as used previously. In books like "Takemusu Aiki" it seems to me that he was saying that the difference is that "aiki", which is a technical principle in arts like Daito-ryu, is expanded to a "philosophical" principle in Aikido. In other words, that the technical principle related to physical interaction between the attacker and attacked changed (or was extrapolated) into a principle related to the interaction with other people on an individual and societal level. In that sense, you could say that Aikido is the only art that teaches "aiki" on both a technical and a philosophical level (at least, ideally).

That Aikido may not offer anything that isn't available elsewhere is, IMO, not all that relevant. There is nothing, at one level, in a chicken that doesn't exist in a dog, but that doesn't mean that they are equivalent.